Urban Ecological Green Space System Construction: Plant Selection and Greening Project Establishment

Author: Lu Min Li Yingjie
Publisher:
Publish Date: 2005-06-01
Features: The Ecological Functions of Urban Greening Plants in City Green Spaces
Urban greening plants are the main materials constituting garden landscapes and the primary plant communities that realize the functional and greening benefits of gardens. Garden trees refer to the woody plants in urban flora, including trees, shrubs, and lianas. Some people compare trees to the "skeleton" or main body of garden landscapes, shrubs to the "muscles" or secondary body, and lianas to the "tendons" or supporting body. On a macro scale, the core of urban greening work lies in urban plants, with garden trees accounting for the largest proportion. In terms of garden construction trends, it is inevitable that plant-based landscaping will be the primary focus. Therefore, urban plants—garden trees—hold a very important position in urban environmental construction and garden greening. Fully understanding, scientifically selecting, and reasonably applying urban plants is of great significance for improving the greening and beautification levels of urban and rural landscapes, purifying the urban environment, enhancing urban natural ecological balance, and fully utilizing the comprehensive functions and benefits of gardens.
Section 1: The Purifying Effects of Garden Plants
1. Absorption of Toxic Gases
Due to environmental pollution, harmful gases in the air have increased, mainly including sulfur dioxide, chlorine gas, hydrogen fluoride, ammonia gas, mercury, and lead vapor. Sulfur dioxide is particularly notorious as the "culprit" of air pollution, being the most abundant, widely distributed, and highly harmful pollutant in the atmosphere. Garden plants act as the largest "air purifiers." The leaves of urban greening plants can absorb sulfur dioxide, hydrogen fluoride, chlorine, and benzopyrene, a carcinogenic substance, among other harmful gases, either by absorbing them or by accumulating them in their bodies to reduce the concentration of toxic substances in the air.
1.1 Sulfur Dioxide
After sulfur dioxide is absorbed by leaves, it forms sulfurous acid and highly toxic sulfite ions within the leaves. These sulfite ions can be oxidized by the plant itself into sulfate ions, which are 30 times less toxic, thus achieving detoxification without harm or reduced harm. The ability of different tree species to absorb sulfur dioxide varies. For example, a pine forest can absorb 20 mg of sulfur dioxide from 1 cubic meter of air per day; a larch forest covering 1 hectare can absorb 720 kg of sulfur dioxide annually; and a weeping willow covering 1 hectare can absorb 10 kg of sulfur dioxide per month during the growing season.
Extensive research has been conducted on the ability of plants to absorb sulfur dioxide, revealing that sulfur dioxide in the air is primarily absorbed by the surfaces of various objects, while plant leaves have a particularly strong capacity for absorbing sulfur dioxide. Sulfur is one of the essential elements for plants, and under normal conditions, plants contain a certain amount of sulfur. However, in sulfur dioxide-polluted environments, the sulfur content in plants can be 5 to 10 times higher than their normal levels. Studies show that the concentration of sulfur dioxide in the air above green spaces is lower than that above non-greened areas. In polluted areas, the sulfur content in tree leaves is many times higher than in clean areas. Within the tolerance range of plants, their absorption capacity increases with higher concentrations of sulfur dioxide in the air. A larch forest covering 1 hectare can absorb 60 kg of sulfur dioxide per day, while a pine forest can absorb 20 mg of sulfur dioxide from 1 cubic meter of air per day. Research also indicates that plants with higher resistance to sulfur dioxide generally absorb more of it. Broadleaf trees are more resistant to sulfur dioxide than coniferous trees. Measurements show,